Lab Report Day Five - Nodal Analysis Lab

Today, we are going to use nodal analysis method for solving circuit problem. To check if we get how to use nodal analysis, we first do a pre-lab and find the theoretical value, and compare it to our experimental value, and find the percent difference. 

 

 

Here is our work for the pre-lab.

 

 

Two group members are doing this pre-lab, to make sure we can get the right theoretical value. And our values match. 

 

 

While setting up the experiment, we first want to use a switching power supply as one of our voltage source. Then professor Mason tells us that it will also add current to the circuit. So with the help of our classmates, I learn how to use waveform. 

This is wrong.

 

 

This is the set up of this experiment. We just build it like the circuit in pre-lab.

 

We measure the true values of our three resistors. 

 

Our measured data. 

We get 2.44 V and 4.43 V. Our theoretical value is 2.424 V and 4.424 V. 

% difference = (2.424-2.44)/2.424*100% = -0.660%

% difference = (4.424-4.43)/4.424*100% = -0.136%

 We get our % difference in less than 1%. This is not exactly 100% same as theoretical value because the resistor we are using are a little bit off. Overall, this experiment is a good experiment, and the results are reasonable.

 

Summary:

In today’s lab, we learn how to do nodal analysis. It simplifies the way we solve the equations, while requires more thinking. We also learn mesh analysis. After, we use what we’ve learned in class to practice with a lab and do fine on the lab.

 

 

 

 

 

 

Lab Report Day Four - Temperature Measurement System

1. In the beginning of the class, we finish a quiz about experiencing the different between KCL and Nodal analysis. (in another blog)

 2.  Temperature Measurement System
In this lab, we will design a circuit that has an output voltage depending on temperature. We are going to use a  thermistor,  which changes resistance when temperature changes, and a known resistance in the circuit.
The pre-lab of the experiment. At room temperature, it has 11000 ohm resistance. At body temperature, it has 7000 ohm resistance. We first find the range of the fixed resistor we are going to use. Since we want the temperature drop to be bigger than 0.5 degrees, we find that the value of the fix resistor must be from 4367 ohm to 17633 ohm.

 

We choose a 5.6 k ohm resistor. The actual resistance of it is 5.49 k ohm.

 

 The power supply is 5.0 V.

 

The set up of the experiment. We measure the voltage across the resistor when it is at room temp to be 3.38 V. 

 

 

We measure the voltage across the resistor when it is at body temp to be 2.68 V. 

 

LAB data table: We have a difference in voltage of 0.7 V, which is bigger than 0.5 V. However, our theoretical value of voltage drop should be 0.533 V, so it has a % difference of -31.3%. I guess what causes this happening could be either the room temperature is lower than 25 degrees, or I am too warm (hotter than 37 degrees).

 

Post lab of this experiment. 

We are then asked to design a new circuit that the output sensitivity of the device must be at least 0.1 V/degree. After our calculation, we find that it is impossible to get it. The maximum we can get a difference of 0.563 V in 12 degree’s difference. Our lab data is bigger than the maximum probably the difference in our temperature is higher than 12 degrees. 

 

Here is a video about our experiment. 

 

Summary

Today, we talk more about nodal analysis. We find that using nodal analysis make us have less algebra to do.We use a thermistor that can change its resistance when temperature changes in lab. 

Quiz 1

In the beginning of class, we are asked to do a quiz. But since we messed up with the current flowing on the resistor in class, after class, we redo the question using the same method. 

 

This is our new result. We count the current multiple times in the first time. 

Lab Report Day Three - Hotdog, Dusk-to-Dawn Light

1. In the beginning of class, Professor Mason brings some hotdog, and try to cook the Hot Dog
a.) He attach a hotdog to a line cord and apply a 120 V potential across it.
We predict that nothing will happen. But based on the experiment,  it seems that we are wrong.

The hot dog is being slowly cooked.

Here is a cool video about a hotdog being cooked by applying 120 V potential. 

b.) Then, we have some parallel and some perpendicular LEDs on the hotdog. We are asked to predict what will happen when we apply a 120 V potential.
Answer is B. The LEDS parallel to the hotdog will light.

In the hotdog, when we apply a 120v potential on it, it will spread equally. When the LED is perpendicular to the hotdog, the potential has no difference, while when the LED is parallel to the hotdog, there is some potential difference existing. The potential difference makes the LED light up.

 

2.  Dusk-to-Dawn Light

In this lab, we are asked to build up a circuit which the LED in it only lights up when it is dark. Being able to do it, we need a bipolar junction transistor (BJT), and a photocell, which is a light sensible resistor. The current in the BJT can only flow when there is a voltage bigger than 2 V applying on it. When it is dark, the photocell has a high resistance, resulting of a high voltage. When it is light, it has a low resistance, resulting of a low voltage. Thus, the BJT acts like a switch.
This is the pre-lab of this experiment. We are asked to calculate the actual voltage across the photocell. When it is dark, it has a resistance of 20k, and has a voltage of 3.33v, which is higher than 2 v.  When it is light, it has a resistance of 5k, and has a voltage of 1.67v, which is lower than 2 v.

This is the set up of the experience. At room light, it does not light up.

When we cover the photocell with sleeves, it starts to light up.

 When it gets dark, it starts to light up.

 

 

 

 

 

 

This is the voltage across the resistor when there’s light. Our experimental value is 1.82 V, while our theoretical value is 1.67 V. 

% difference: (1.67-1.82)/1.67*100%=-8.98%

There is difference probably because the room light is darker than our theoretical light. 

 

 The voltage of it across the resistor when it is dark. 

Our experimental value is 2.60 V, while our theoretical value is 3.33 V. 

% difference: (3.33-2.60)/3.33*100%=21.9%

There is difference probably because the brightness in the sleeves is brighter than our theoretical light. 

 

Here is a video about our experiment.

 

Summary

Today we learn more with Kirchhoff’s Law. We do an amazing experiment to cook a hot dog with electricity, and let the LED light on the hot dog. We learn how night light works and talk about BJT.

Lab Report Day Two - Ohm's Lar, Dependent Sources and MOSFETS

 

1.In the beginning of class, we are asked to make a prediction about what will happen if the switch is closed in the circuit shown below. 

 

 

We make a prediction that both the upper light bulb and the lower light bulb will stay the same. 

 

 

 

 

As we can see from the picture, the brightness of the two bulb stay unchanged. Our prediction is correct.  Since the two bulbs are identical, we assume that the power supply (the two batteries) is 3V. So on each bulb, it is 1.5V. When we connect a battery in parallel with one of them, the voltage in the circuit stays the same. Since P=V^2/R, we can say that the power of both bulb stay unchanged as long as the resistance of the two bulbs is constant. Therefore, the brightness of the two light bulb does not change. 

 

2. In this lab, we use WaveForm as power supply that can have various voltage value through a 100 ohm resistor. 

 

Here is the circuit. We are going to measure the current across the resistor. 

 

The set up of the experiment.

 

Our data table

 

We measure the real value of the resistor, and it shows that it is 100.9 ohm. We apply different voltages across the resistor with WaveForms and measure the current for each voltage.

 

The graph of Voltage vs. Current. It is a linear relationship, and it follows the Ohm's law, the relationship between current and voltage, V=IR. 

In the graph, the slope 103.6 should be the resistance of the resistor. It's bigger than 100.9 ohm, which means the wires in the circuit has a small value of resistance.

 

% difference is (100.9-103.6)/100.9*100% = -2.67%

 

 

3. In this lab, we are going to use a MOSFET and a 100 ohm resistor. We have a resistor which has a true value of 100.9 ohm. We are going to determine the threshold voltage of the MOSFET. If the voltage is below the gate voltage, there won’t be any significant current. With MOSFET, we can increase the power supply’s current by increasing the gate voltage. A MOSFET and a power supply, can act as a voltage controlled current source in which the drain current is controlled by the gate voltage.

 

 The set up of the experiment. We at first use the regular power supply. After figuring how to use the waveform, we do a new experiment with waveform.

The circuit of the experiment

The data table of our experiment. We connect a 5 V voltage supply in the circuit, and apply different voltages to the MOSFET. As we can see, the current starts increasing significantly between 2.0V and 2.2V. So we guess the gate voltage is 2.2 V. 

Gate Voltage vs. Drain Current Graph.

From the graph, we can see the threshold voltage is around 2.2 V.  When the voltage is below 2.2 V, it increases slowly. When it is greater than 2.5 V, it increases slowly again. So the starting point which it increases rapidly is the threshold voltage. 

The dependent source is a VCCS (voltage controlled current source). The current of it is controlled by the input voltage.

When I try to fit a straight line, I get an estimated value of g for 0.0355. 

Summary:

In today’s lab, we review Ohm’s Law and Kirchhoff’s Laws. We learn a little about depend source, and one of it, voltage controlled current source (VCCS). 

 

 

 

 

FreeMAT (only need first two assignment)

The purpose of this lab is an introduction to using the program FreeMat.

 

Solving Simultaneous Equations with MATLAB


Assignment 1

 

ADDING SINUSOIDS

 

Assignment 1

1. 

The circuit with time constant 100ms will have lower output.

 

 2. 

Assignment 2
1. 

When two sine waves adding together, the result is still a sine wave. 

2. 

 

Functions to convert form rectangular to polar (due after the first celebration)

 

Assignment

1-3

 

 

 

4

 

 

 

SOLVING FOR ROOTS OF EQUATIONS

 

Assignment 1

Assignment 2

 

 

 

Lab Report Day One - Solderless Breadboards, Open-Circuits and Short-circuits

In today's lab, we are going to use Digital Multimeters (DMMs) to measure the resistance between the holes. Those holes could be in either same node, or in different node but in same row, or in different row, or finally connect two nodes in different rows and measure the resistance between them. We are told that when the resistance is close to 0, it is short-circuit.When the resistance is close to ∞, it is open-circuit.


1. First, we use DMM to measure the resistance between two holes in the same node on the breadboard. Just as the instruction said, we had a very low resistance between the holes. We get 4.6Ω.
Based on what we learn, it is short-circuit.




2. Then, we use DMM to measure the resistance between two holes in the same row but in different node on the breadboard. Just as the instruction said, we had a very high or infinite resistance between the holes. We get ∞ Ω. The measurement goes all the way from 1 M to 19 M and finally goes to 1, which is too large to measure. We consider this infinite. 
Based on what we learn, it is open-circuit.




3. Then, we use DMM to measure the resistance between two arbitrary holes in the different row on the breadboard. Just as the instruction said, we had a very high or infinite resistance between the holes. We get ∞ Ω. The measurement goes all the way from 1 M to 19 M and finally goes to 1, which is too large to measure. We consider this infinite. 
Based on what we learn, it is open-circuit.




4. Finally, we use DMM to measure the resistance between two different rows on the breadboard with a jumper wire connect the two nodes. Just as the instruction said, we had a very low resistance between the holes. We get 4.6Ω.
Based on what we learn, it is short-circuit.


How we connect the DMM to the breadboard.
The resistance we get.


5. Result for lab


Here is the result we get from the four experiment. (The (A) part from the previous pictures should be 4.6 since we misread it.)

We can conclude that in a breadboard, it is short-circuit in the same node or when the two nodes are connected together with a jumper wire. It is open-circuit in different nodes, no matter they are in same rows or different rows.

Summary:

Today, we review some knowledge we previously learned from PHYSICS 4B. We  know how to measure a circuit is short-circuit or open-circuit. We also learn some basic property of breadboard.